Cocatalytic composition which is usable for the polymerization of alpha-olefins

ABSTRACT

Cocatalytic composition resulting from bringing an organoaluminium halide (A) into contact with an electron-donating organic compound (ED) selected from esters, amides and ketones, the organoaluminium halide (A) possessing an atomic ratio halogen (X)/aluminium (Al) of greater than 1 and less than 1.3, the halide (A) and the compound (ED) being employed in a mole ratio halide (A)/compound (ED) of greater than 20. 
     Catalytic systems which are usable for the polymerisation of alpha-olefins, comprising such a cocatalytic composition--and a solid based on titanium trichloride complexed with an electron-donating compound.

The present invention relates to cocatalytic compositions which areusable for the polymerisation of alpha-olefins. It also relates tocatalytic systems comprising these compositions, as well as to solidscontaining a titanium halide. It further relates to a process for thepolymerisation of alpha-olefins, especially for the stereospecificpolymerisation of propylene, performed in the presence of these systems.

It is known to polymerise alpha-olefins such as propylenestereospecifically by means of catalytic systems comprising a cocatalystconsisting of an organometallic compound, such as an optionallyhalogenated alkylaluminium compound, together with a solid constituentcontaining a titanium halide.

It is known that, among halogenated alkylaluminium compounds,alkylaluminium dihalides are not suitable for the stereospecificpolymerisation of alphaolefins except when electron-donating compoundsare added to them (A. D. Ketley, The Stereochemistry of Macromolecules,volume 1, 1967, pages 24 and 27). The halogenated alkylaluminiumcompounds which are preferred, because they confer maximumstereospecificity on the abovementioned catalytic systems, aredialkylaluminium halides purified so as to remove from them harmfulimpurities such as trialkylaluminiums and dialkylaluminium hydrides[see, for example, U.S. Pat. No. 3,100,218 (MONSANTO CHEM. CO.)].

Numerous catalytic systems of this type are described in the literature.For example, a description has been given in Patent CS-A-120,142 (JIRIMEJZLIK et al.), as summarised in Chemical Abstracts, volume 68, 1968,page 5, reference 65996 g, of the polymerisation of propylene in thepresence of a catalytic system comprising a titanium trichloride anddiethylaluminium chloride with the addition of 1 to 30% of the weight ofthe latter of ethylaluminium dichloride. The increase instereospecificity obtained is accompanied by a decrease in productivity.

In U.S. Pat. No. 4,400,494, a description has been given of thepolymerisation of propylene in the gaseous phase in the presence of acatalytic system comprising a constituent containing reduced titaniumand an alkylaluminium halide in which the atomic ratio halogen/aluminiumis between 0.89 and 0.98. The presence of additives supplementing thesesystems, recommended in this patent (column 5, lines 26 to 38), makesthem unstable.

Moreover, Example 1 of Patent Application EP-A-0,069,461 (TOA NENRYOKOGYO) describes the polymerisation of propylene in the presence of asystem comprising a solid catalytic constituent based on complexedtitanium trichloride, diethylaluminium chloride and ethyl benzoate,diethylaluminium chloride being used in the proportion of 15 moles pergram-atom of titanium present in the solid catalytic constituent, andethyl benzoate in the proportion of 0.02 mole per mole ofdiethylaluminium chloride. The polymer obtained must be purified inrespect of catalytic residues.

A description has also been given, in the publication of PatentApplication JA-A-7231703 (TOKUYAMA SODA), of the polymerisation ofpropylene in the liquid monomer in the presence of a mixture of titaniumtrichloride and a dialkylaluminium halide, to which were added 0.001 to0.1 mole of alkylaluminium dihalide per mole of dialkylaluminium halideand, optionally, a compound selected from polyamides and polyethers.While these systems appear to improve the mechanical properties of thepolymer obtained, the incorporation of the alkylaluminium dihalide hasno beneficial effect on stereospecificity. It is found, in addition,that the productivity of the catalytic system decreases when thequantity of alkylaluminium dihalide increases.

French Patent Application FR-A-2,551,759 (NORTHERN PETROCHEMICAL Co.)describes the polymerisation of propylene in the presence of a catalyticsystem formed by successively mixing a compound comprising titaniumtrichloride cocrystallised with aluminium trichloride, modified bygrinding with butyl benzoate and washed with liquid propylene, butylbenzoate and diethylaluminium chloride. To increase the productivity ofthese catalytic systems, an ethylaluminium chloride of atomic ratio(Cl)/(Al) less than 1 is used.

Most of the catalytic systems described above involve the polymerisationof propylene in the presence of a catalytic solid based on a titaniumhalide, a halogenated organoaluminium compound and an electron-donatingcompound. Given their industrial importance, these catalytic systems,and especially mixtures comprising an organoaluminium compound and anelectron-donating compound, have been the subject of numeroustheoretical studies (see, for example, S. Pasynkiewicz, Pure Appl.Chem., 1972, 30, pp. 509-521 and K. B. Starowieyski et al., J.Organomet. Chem., 1976, 117, pp. C1 to C3). It emerges from thesestudies that bringing an organoaluminium compound into contact with anelectron-donating compound gives rise to the formation of unstablecomplexes which degrade to form a complex mixture which changes overtime. The preparation of such solutions a long time before their use inpolymerisation is consequently difficult to envisage.

The present invention is directed towards the provision of cocatalyticcompositions capable of being stored for fairly long periods withouttheir catalytic efficacy being impaired, and which do not possess thedrawbacks inherent in the use of known catalysts possessing excellentcatalytic properties.

It has thus been found that the combination of certain halogenatedorganoaluminium compounds with particular electron-donating organiccompounds in specified ratios leads to new cocatalytic compositionswhich are easy to use in polymerisation and whose catalytic efficacy isnot impaired during storage for several weeks or even several months.

It has also been found that the combination of these compositions withcertain catalytic solids containing a titanium halide enables catalyticsystems providing for an ideal compromise between productivity andstereospecificity to be obtained without the need to employ largequantities of electron-donating compound.

The present invention consequently relates, as its main feature, to acocatalytic composition resulting from bringing an organoaluminiumhalide (A) into contact with a particular electron-donating organiccompound (ED) selected from esters, amides and ketones, theorganoaluminium halide (A) possessing an atomic ratio halogen(X)/aluminium (Al) of greater than 1 and less than 1.3, the halide (A)and the compound (ED) being employed in a mole ratio halide (A)/compound(ED) of greater than 20.

The organoaluminium halide (A) which is usable for preparing thecocatalytic composition according to the invention may be represented bythe overall formula: ##STR1## in which R¹ and R² represent identical ordifferent hydrocarbon radicals selected from alkyl, alkenyl, cycloalkyl,aryl, arylalkyl, alkylaryl, alkoxy and aryloxy radicals;

X is a halogen;

m and n each represent any number such that 0≦m<2 and 0≦n<2, and prepresents a number such that 1<p<1.3, the sum of m, n and p equalling3.

In the formula (I), R¹ and R² are preferably selected from alkyl, alkoxyand aryloxy radicals, X is preferably chlorine, m preferably representsa number such that 1≦m≦1.95 and p preferably represents a number suchthat 1<p<1.15.

In the formula (I), R¹ may be selected most especially from linear orbranched alkyl radicals containing from 2 to 8 carbon atoms and R² mostespecially from these radicals and optionally substituted aryloxyradicals containing from 6 to 35 carbon atoms.

In the formula (I), p is generally greater than 1.005, preferablygreater than 1.01 and most especially greater than 1.015. In thisformula (I), p is generally less than 1.1, preferably less than 1.08 andmost especially less than 1.06.

As shown, in particular, by the values assigned to p in the formula (I),the organoaluminium halide (A) which is usable according to theinvention is not a pure, defined organoaluminium compound but a mixtureof different organoaluminium compounds in quantities suitable forobtaining compositions possessing an atomic ratio (X)/(Al) of greaterthan 1 and less than 1.3 and whose empirical structure corresponds tothe formula (I).

As examples of halides (A) corresponding to the overall formula (I),there may be mentioned alkylaluminium halides such as ethyl-, n-propyl-and i-butylaluminium chlorides, ethylaluminium fluorides, bromides andiodides, alkoxyaluminium halides such as ethoxyaluminium chlorides andmixtures of the above compounds in suitable proportions.

Other examples of halides (A) comprise alkylalkoxyaluminium halides andalkylaryloxyaluminium halides; these compounds may be obtained in aknown manner by reaction of halogenated alkylaluminium compounds with analcohol, a phenol or oxygen; as alkylalkoxyaluminium halides which areusable, ethylethoxyaluminium chloride, isobutylethoxyaluminium chloride,ethylbutoxyaluminium chloride and mixtures thereof may be mentioned; asalkylaryloxyaluminium halides which are usable, ethylphenoxyaluminiumchloride may be mentioned.

A special class of halides (A) comprises the products of the reaction ofhalogenated alkylaluminium compounds with hydroxyaromatic compounds inwhich the hydroxyl group is sterically hindered, as well as mixtures ofthese products with the halogenated alkylaluminium compounds from whichthey are derived.

The hydroxyaromatic compounds in which the hydroxyl group is stericallyhindered are generally selected from mono- or polycyclic hydroxyarylenessubstituted with a secondary or tertiary alkyl radical in both orthopositions with respect to the hydroxyl group, and preferably fromphenols di-tert-alkylated in the ortho positions with respect to thehydroxyl groups and esters of3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid. Among thesecompounds, the best results have been obtained with n-octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate and with2,6-di-tert-butyl-4-methylphenol.

To obtain such organoaluminium halides (A), the halogenatedalkylaluminium compound having a suitable halogen content and thehydroxyaromatic compound may be brought into contact beforehand in themole ratio halogenated alkylaluminium compound/hydroxyaromatic compoundof between 100 and 1, preferably between 60 and 5 and especially between50 and 10, in an inert hydrocarbon diluent, for the time needed for atleast partial formation of the said reaction product, which can takebetween 5 minutes and 24 hours and is most often accompanied by anevolution of gas, enabling the progress of the reaction to be assessed.

Among all the organoaluminium halides (A) defined and listed above, thebest results are obtained with alkylaluminium chlorides (A), especiallywith ethylaluminium chlorides, possessing an atomic ratiochlorine/aluminium of greater than 1.005, preferably greater than 1.01and more especially greater than 1.015, and less than 1.1, preferablyless than 1.08 and more especially less than 1.06. These chlorides maybe obtained by mixing in suitable proportions alkylaluminium mono- anddichloride or trialkylaluminium and alkylaluminium dichloride, the alkylradicals of these compounds preferably being identical and typically anethyl radical.

The particular electron-donating organic compound (ED) which is usablefor preparing the cocatalytic composition according to the invention isselected from esters, amides and ketones. The esters and amides can beesters and amides of mono- and polycarboxylic acids, in particularesters and amides of aliphatic carboxylic acids, esters and amides ofolefinic carboxylic acids, esters and amides of alicyclic carboxylicacids and esters and amides of aromatic carboxylic acids. Esters of3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionicacid, mentioned above, arealso suitable. The amides can be mono- or disubstituted on the nitrogenatom, in particular with alkyl and phenyl radicals.

As esters which are usable, there may be mentioned methyl acetate, ethylacetate, phenyl acetate, ethyl chloroacetate, methyl propionate, ethylbutyrate, ethyl valerate, methyl acrylate, ethyl acrylate, methylmethacrylate, ethyl benzoate, butyl benzoate, methyl toluate, ethyltoluate, ethyl anisate, diethyl succinate, dibutyl succinate, diethylmalonate, dibutyl malonate, dimethyl malonate, dibutyl maleate, diethylitaconate, dibutyl itaconate, monoethyl phthalate, dimethyl phthalate,ethylmethyl phthalate, diethyl phthalate, di-n-propyl phthalate,diisobutyl phthalate, di-n-hexyl phthalate, di-n-octyl phthalate anddiphenyl phthalate.

As amides which are usable, there may be mentioned formamide, acetamide,propionamide, n-butyramide, n-valeramide, n-caproamide, lauramide,stearamide, dimethylformamide, N-methylacetamide, N,N-dimethylacetamide,chloroacetamide, acrylamide, methacrylamide, β,β-dimethylacrylamide,adipamide, benzamide, phthalamide, N,N-dimethylbenzamide, benzanilideand N,N-diphenylbenzamide.

As ketones which are usable, there may be mentioned acetone, methylethyl ketone, methyl isobutyl ketone, acetylacetone, propiophenone,acetophenone and benzophenone.

Very good results are obtained with esters of aromatic carboxylic acids,such as benzoates, toluates and phthalates. The amides derived fromaromatic carboxylic acids, such as benzamide or phthalamide, substitutedor otherwise, are also very suitable. Advantageously, electron donorswhich are liquid at room temperature are used. Liquid aromaticcarboxylic acid esters are very suitable. It is preferable to use anaromatic carboxylic acid ester which is soluble in alkylaluminiumcompounds. Ethyl benzoate is most especially preferred as anelectron-donating compound (ED).

It is self-evident that, for the preparation of the cocatalyticcomposition according to the invention, the use of severalorganoaluminium halides (A) and several electron-donating compounds EDis in no way ruled out.

The general conditions of formation of the cocatalytic compositionaccording to the invention are not critical, insofar as they lead to afinal product containing a large excess, as defined below, of the halide(A) relative to the compound (ED).

In general, contact of the halide (A) and the compound (ED) with oneanother is established in the liquid phase. Since the cocatalyticcomposition of the invention consists essentially of the productresulting from bringing the halide (A) and the compound (ED) intocontact, this contacting is performed under non-polymerising conditions,that is to say in the absence of polymerisable alpha-olefin and/or ofcatalytic solid containing a titanium halide.

This contacting may be carried out in the presence of an inert diluent.In this case, a diluent is selected in which at least one of thecompounds involved is soluble. When a diluent is used, it is preferablethat the total concentration of dissolved compounds is not less than 5%by weight, and especially preferable that it is between 5 and 20% byweight. This diluent is generally selected from liquid aliphatic,cycloaliphatic and aromatic hydrocarbons such as liquid alkanes,isoalkanes and cycloalkanes and benzene.

The halide (A) and the compound (ED) which are preferred according tothe invention are soluble in these diluents.

It is also possible to carry out the contacting of the halide (A) andthe compound (ED) with one another, and this constitutes a preferredembodiment of the invention, in the absence of a diluent, by selectingtemperature and pressure conditions such that at least one of thecompounds involved is in the liquid state. The halide (A) and thecompound (ED) are often liquid, and/or each of them often capable ofdissolving the other under normal temperature and pressure conditions .Under these same conditions, the cocatalytic composition obtained itselfoften also takes liquid form. Preferably, this cocatalytic compositiontakes the form of a homogeneous liquid. This form is advantageousinasmuch as it permits the storage, transport and ready handling of thecocatalytic compositions in small volumes. It is also advantageous inthe context of the use of these compositions in polymerisation processesperformed without a diluent, especially in the processes ofpolymerisation of propylene performed in the monomer maintained in theliquid state or in the gaseous phase.

As regards the method of bringing the halide (A) and the compound (ED)into contact to form the cocatalytic composition according to theinvention, account should be taken of what has been mentioned above,namely that the halide (A) is not a pure, defined compound but resultsfrom the mixing of organoaluminium compounds in proportions selected tolead to an atomic ratio (X) (Al) of greater than 1 and less than 1.3 andso that their empirical composition corresponds to the formula (I). Ifhenceforward a less halogenated or unhalogenated organoaluminiumcompound used for preparing the halide (A) is designated (AA) and a morehalogenated organoaluminium compound used for preparing the halide (A)is designated (AB), it is possible:

to bring the compound (ED) into contact with the halide (A) preformed byprior mixing, in appropriate quantities, of the compounds (AA) and (AB);

when the compound (AB) is present in excess relative to the other two,to introduce into it, successively and in appropriate quantities, thecompound (AA) for the "in situ" formation of the halide (A) and then thecompound (ED); or to introduce into it, successively and in appropriatequantities, the compound (ED) and then the compound (AA).

The first method of formation of the cocatalytic composition definedabove is the preferred one.

The compounds involved in the formation of the cocatalytic compositionaccording to the invention are brought into contact with one another attemperatures generally between approximately 0° and 90° C., andpreferably at a temperature in the region of room temperature (25° C.).

The use of the halide (A) and the compound (ED) for preparing thecocatalytic composition according to the invention is implemented in thehigh mole ratio halide (A)/compound (ED) mentioned above.

This mole ratio of the halide (A) to the compound ED) is greater than 20and preferably greater than 30. This mole ratio is advantageouslygreater than 35 and most often greater than 50, the best results beingobtained when it is at least 52. In general, the mole ratio (A)/(ED)does not exceed approximately 150, and it often does not exceedapproximately 90. In most cases, the mole ratio (A)/(ED) does not exceed75.

The mole ratios (A)/(ED) can thus be generally between 35 and 150, andoften between 40 and 90. When the halide (A) and the compound (ED) areemployed in the form of undiluted liquids to obtain a liquid cocatalyticcomposition, these mole ratios are often greater than 50 and preferablyat least 52 without exceeding 90, and most especially between 52 and 75.The cocatalytic compositions which yield the bestproductivity/stereoselectivity compromise are obtained by adding aliquid aromatic carboxylic acid ester, and more especially ethylbenzoate, to an alkylaluminium chloride of atomic ratio (Cl)/(Al)between 1.01 and 1.06, in proportions such that the mole ratio halide(A)/compound (ED) is between 52 and 75.

The preparation of the cocatalytic composition according to theinvention can advantageously be completed by maintaining it at roomtemperature (approximately 25° C.) for a period of at least 30 minutes(ageing phase) when it is intended that it should be brought intocontact, as soon as its preparation is complete, with a solidconstituent containing a titanium halide. The ageing phaseadvantageously lasts at least approximately 1 hour at room temperature.The cocatalytic composition thereby obtained possesses a complexchemical composition which is variable over time, resulting from thecomplexing reactions between the different constituents and from thedegradation of these complexes. Despite these different reactions, thecocatalytic composition of the invention may be stored without losingits catalytic properties.

Thus, it may be stored for several months, up to temperatures of theorder of 50° C., without its catalytic properties being substantiallymodified.

The cocatalytic compositions described above may be used, and thisconstitutes a second aspect of the invention, in combination with solidscontaining a titanium halide, to form catalytic systems which are usablefor polymerising alpha-olefins.

The titanium halide contained in these solids can be the mainconstituent thereof or can represent only a part, even a minor part, ofthe total chemical composition of these solids. This titanium halide ispreferably a chloride, especially a tetra- or trichloride.

Examples of solids in which the titanium halide represents only a minorpart in the chemical composition are so-called "supported" catalysts.The support for the halide is generally inorganic in nature. Magnesiumhalides, especially magnesium chlorides, the X-ray diffraction spectrumof which differs from the normal spectrum of this compound, arefrequently used for this purpose.

Both the support and the titanium halide can be combined with or cancontain electron-donating compounds, especially esters.

Examples of solids in which the titanium halide is the main constituentare solids in which more than 50% of the total weight, and often morethan 60% of the total weight, consists of solid titanium halide.Preferably, this halide is titanium trichloride, most especiallytitanium trichloride complexed with an electron-donating compound. Thesesolids are preferred as constituents of the catalytic systems accordingto the invention.

These solids may be obtained by any known process.

It is generally preferably to use a solid obtained by a processinvolving an initial reduction of a titanium compound selected from thetetrahalides and compounds of the tetra(hydrocarbon radical-oxy)titaniumtype and mixtures thereof. As examples of titanium tetrahalides, thetetraiodide, tetrabromide and tetrachloride may be mentioned. Asexamples of compounds of the tetra(hydrocarbon radical-oxy)titaniumtype, there may be mentioned the tetraalkoxides such as tetramethoxy-,tetraisopropoxy- and tetra-n-butoxytitaniums; and the tetraaryloxidessuch as tetraphenoxy-, tetracresyloxy- and tetranaphthyloxytitaniums,for example.

Among the titanium compounds mentioned above, preference is given to thetitanium tetrahalides, and among the latter, titanium tetrachloride.

The reduction may be performed with the participation of hydrogen or ofmetals such as magnesium and, preferably, aluminium, especially when thetitanium compound is a titanium tetrahalide. It is neverthelesspreferable to perform the reduction of the titanium compound withparticipation of an organometallic reducing agent, which can be, forexample, an organomagnesium reducing agent.

The best results are obtained when the reduction of the titaniumcompound is performed with the participation of organoaluminium reducingagents.

The organoaluminium reducing agents which are preferably usable arecompounds which contain at least one hydrocarbon radical bound directlyto the aluminium atom. Examples of compounds of this type are mono-, di-and trialkylaluminiums in which the alkyl radicals contain from 1 to 12,and preferably from 1 to 6, carbon atoms, such as triethylaluminium, theisoprenylaluminiums, diisobutylaluminium hydride andethoxydiethylaluminium. With the compounds of this type, the bestresults are obtained with alkylaluminium chlorides, especially withdiethylaluminium chloride and with ethylaluminium sesquichloride.

To obtain the solid constituents of the catalytic systems which areusable according to the invention, the reduced solids mentioned aboveare subjected to a treatment by means of at least one complexing agent,which is generally selected from organic compounds comprising one ormore atoms or groups possessing one or more lone pairs of electronscapable of providing for coordination with the titanium or aluminiumatoms present in the titanium or aluminium compounds defined above.Preferably, the complexing agent is selected from the family ofaliphatic ethers, and more especially from those in which the aliphaticradicals comprise from 2 to 8 carbon atoms, and preferably 4 to 6 carbonatoms. A typical example of an aliphatic ether giving very good resultsis diisoamyl ether.

These treatments by means of complexing agents, designed to stabilise orimprove the productivity and/or stereospecificity of the catalyticsolids, are well known and have been fully described in the literature.

Thus, the treatment by means of the complexing agent may consist ingrinding the reduced solid in the presence of the complexing agent. Itmay consist of a thermal treatment of the reduced solid in the presenceof the complexing agent. It may also consist of extractive washes ofreduced solid in the presence of mixed solvents comprising a liquidhydrocarbon compound and a polar auxiliary solvent, for example anether. It is also possible to perform the reduction of the titaniumcompound, especially the tetrachloride, with the organoaluminiumreducing agent in the presence of the complexing agent, for example byadding to the titanium tetrachloride a solution in a hydrocarbon of theproduct of the reaction of the complexing agent with this reducingagent, and then to subject the reduced solid thereby obtained to athermal treatment in the absence of complexing agent, or in the presenceof a further quantity of complexing agent identical to or different fromthe previous one. It is also possible to perform the treatment by meansof the complexing agent with a quantity of the latter sufficient to forma homogeneous solution of solid based on titanium trichloride and toreprecipitate, by heating, the solid thus dissolved.

For the preparation of the solid constituent of the catalytic systemsaccording to the invention, the treatment by means of the complexingagent may be combined with or followed by an activation treatment. Theseactivation treatments are also well known and have also been describedin the literature. They are generally performed by means of at least oneagent selected from inorganic halogen compounds, organic halogencompounds, interhalogen compounds and halogens. Among these agents,there may be mentioned:

as inorganic halogen compounds, metal and non-metal halides such astitanium and silicon halides, for example;

as organic halogen compounds, halogenated hydrocarbons such ashalogenated alkanes and carbon tetrahalides, for example;

as interhalogen compounds, iodine chloride and bromide, for example;

as halogen, chlorine, bromine and iodine.

Examples of agents which are very suitable for the activation treatmentare titanium tetrachloride, silicon tetrachloride, iodobutane,monochloroethane, hexachloroethane, chloromethylbenzene, carbontetrachloride, iodine chloride and iodine. The best results have beenobtained with titanium tetrachloride.

The physical form in which the complexing agents and the agents used forthe possible activation treatment occur is not critical for thepreparation of the precursor. These agents may be employed in gaseousform or in liquid form, the latter being the form they most commonlytake under the usual conditions of temperature and pressure. It is alsopossible to perform the treatment by means of the complexing agent andthe possible activation treatment in the presence of an inerthydrocarbon diluent, such as those defined above in relation to thepreparation of the cocatalytic composition, generally selected fromliquid aliphatic, cycloaliphatic and aromatic hydrocarbons such asliquid alkanes and isoalkanes and benzene.

Details relating to the working conditions for the commonest complexingand activation treatments may be found, in particular, in PatentsBE-A-780,758 (SOLVAY & Cie), BE-A-864,708 (SUMITOMO CHEMICAL COMPANYLTD), U.S. Pat. No. 4,368,304 (CHISSO CORPORATION) and U.S. Pat. No.4,295,991 EXXON RESEARCH AND ENGINEERING CO.), as well as in thedocuments cited in the latter.

At any time during its preparation, after the reduction or complexingstep or after the possible activation step, but preferably after thereduction step, the solid constituent of the catalytic system may besubjected to a treatment aimed at decreasing the friability of itsconstituent particles. This treatment, referred to as"prepolymerisation", consists in bringing the solid into contact with alower alpha-monoolefin such as ethylene or, better, propylene, underpolymerising conditions so as to obtain a solid generally containingbetween 5 and 500% by weight approximately of "prepolymerised"alpha-monoolefin relative to the weight of titanium halide which itcontains. This "prepolymerisation" may advantageously be performed in asuspension of the solid in the inert hydrocarbon diluent as definedabove, for a sufficient time to obtain the desired quantity ofprepolymerised alpha-monoolefin on the solid. The solid constituentcontained according to this variant is less friable, and enablespolymers of good morphology to be obtained even when polymerisation isperformed at relatively high temperature.

In addition, at any time during its preparation, but preferably afterthe activation step when the latter is undertaken, the solid constituentmay be subjected to an additional activation treatment aimed atmaintaining the stability of its properties and/or aimed at increasingits stereospecificity. This additional activation treatment consists inbringing the solid constituent, preferably separated from the medium inwhich it has been prepared and washed with an inert hydrocarbon diluentas defined above, into contact with an activating agent selected fromorganoaluminium compounds and the products of the reaction of anorganoaluminium compound with a compound selected from hydroxyaromaticcompounds in which the hydroxyl group is sterically hindered. Theorganoaluminium compound is preferably selected from trialkylaluminiumsand alkylaluminium chlorides. Among these compounds, the best resultshave been obtained with diethylaluminium chloride. The hydroxyaromaticcompound corresponds to the same definitions and limitations as thosestated above in relation to the nature of the halide (A).

Further details in relation to the additional activation treatmentdefined above, in particular in relation to the nature of theorganoaluminium and hydroxyaromatic compounds, with the workingconditions under which this treatment is performed and with the textureof the preactivated solid obtained, will be found in PatentsBE-A-803,875 (SOLVAY & Cie) and FR-A-2,604,439 (SOLVAY & Cie), thecontent of which is incorporated by reference in the presentdescription.

A preferred method of preparation of the solid participating in thecomposition of the catalytic system which is usable according to theinvention has been described in Patent BE-A-780,758 (SOLVAY & Cie).

This method comprises the reduction of titanium tetrachloride by meansof an organoaluminium reducing agent which, in this instance, ispreferably a dialkylaluminium chloride in which the alkyl chainscomprise from 2 to 6 carbon atoms, under mild conditions. After anoptional thermal treatment of the reduced solid thereby obtained, thelatter is subjected to a treatment by means of a complexing agent asdefined above. Lastly, a treatment by means of titanium tetrachloride iscarried out, and the solid based on complexed titanium trichloridethereby formed is separated and washed, generally be means of an inerthydrocarbon diluent as defined above, preferably selected from liquidaliphatic hydrocarbons comprising from 3 to 12 carbon atoms and whichis, moreover, the diluent which may be used throughout the preparationof the said solid.

The preferred method of preparation defined in the above paragraph leadsto particles of solid based on complexed titanium trichloride which arealso described in Patent BE-A-780,758. These particles are spherical andgenerally have a diameter of between 5 and 100 microns, and most oftenbetween 10 and 50 microns. They consist of an agglomerate ofmicroparticles, also spherical, which have a diameter of between 0.05and 1 micron, and most often between 0.1 and 0.3 micron, and which areextremely porous. As a result, the particles possess a specific surfacearea larger than 75 m² /g and lying most often between 100 and 250 m²/g, and a total porosity larger than 0.15 cm³ /g and mostly between 0.20and 0.35 cm³ /g. The internal porosity of the microparticles constitutesthe largest contribution to this total porosity of the particles, asborne out by the high value of the pore volume corresponding to poresless than 200 in diameter, which is larger than 0.11 cm³ /g and mostlybetween 0.16 and 0.31 cm³ /g.

The solids based on complexed titanium trichloride (constituent (a))obtained according to the method of preparation described in PatentBE-A-780,758, selecting the preferred operating conditions, correspondto the formula:

    TiCl.sub.3.(AlRCl.sub.2).sub.x.C.sub.y

where R is an alkyl radical comprising from 2 to 6 carbon atoms, C is acomplexing agent as defined above, x is any number less than 0.20 and yany number greater than 0.009, and generally less than 0.20.

As variants of this method of preparation, those referred to above maybe mentioned, consisting in:

"prepolymerising" the reduced solid, after the optional thermaltreatment and before the treatment by means of the complexing agent,with a lower alpha-monoolefin (propylene) under polymerising conditions.This "prepolymerisation" is performed in a suspension of the reducedsolid in the inert hydrocarbon diluent as defined above, at between 20°and 80° C. approximately, for a time generally between 1 minute and 1hour;

undertaking an additional activation treatment of the solid, byintroducing a solution of the product of the reaction of theorganoaluminium compound and the hydroxyaromatic compound into asuspension in a hydrocarbon of the constituent (a) then maintained at atemperature preferably of between 20° and 40° C. approximately for atime preferably of between 15 and 90 minutes.

These variants may be employed separately or in combination.

Irrespective of the variant(s) adopted for the preparation of the solidconstituent of the catalytic system, and as mentioned above, the latteris finally separated from its formation medium and generally then washedby means of an inert hydrocarbon diluent of the same nature as thosewith whose participation it has, where appropriate, been prepared.

The solid constituent of the catalytic system which is usable accordingto the invention, separated and washed, may then be optionally dried ina conventional manner, for example according to the method described inPatent BE-A-846,911 (SOLVAY & Cie).

After it has been washed and optionally dried, the solid constituent ofthe catalytic system according to the invention may be immediatelybrought into contact again with an inert hydrocarbon diluent such asthose which have been defined above, and which are also usable asdiluents in the suspension polymerisation. It may be stored in such adiluent or in dry form, preferably in the cold state, for long periods,without losing its qualities. It may also be stored in the form of asuspension in a mineral oil or a silicone oil.

The invention also relates to a process for the polymerisation ofalpha-olefins performed in the presence of the catalytic systemsdescribed above. To this end, the cocatalytic composition and the solidconstituent containing a titanium halide may be brought into contactwith one another before being introduced into the polymerisation medium,or be added separately to this medium.

Precontact, when it is performed, is generally carried out at atemperature of between -40° and 80° C., for a time which is dependent onthis temperature and which can range from a few seconds to several hoursor even several days.

The catalytic systems comprising the solid constituent and thecocatalytic composition, defined and combined as described above, areapplied to the polymerisation of terminally unsaturated olefins, themolecule of which contains from 2 to 18 and preferably from 2 to 6carbon atoms, such as ethylene, propylene, 1-butene, 1-pentene,methyl-1-butene, 1-hexene, 3- and 4-methyl-1-pentenes andvinylcyclohexene. They are especially advantageous for thestereospecific polymerisation of propylene, 1-butene and4-methyl-1-pentene to strongly isotactic, crystalline polymers.

They are also applied to the copolymerisation of these alpha-olefinswith one another, as well as with diolefins comprising from 4 to 18carbon atoms. Preferably, the diolefins are unconjugated aliphaticdiolefins such as 1,4-hexadiene, unconjugated monocyclic diolefins suchas 4-vinylcyclohexene, alicyclic diolefins having an endocyclic bridge,such as dicyclopentadiene and methylene- and ethylidenenorbornene, andconjugated aliphatic diolefins such as butadiene or isoprene.

They are further applied to the manufacture of copolymers referred to asblock copolymers, which are formed from alpha-olefins and diolefins.These block copolymers consist of successions of chain segments havingvariable lengths; each segment consists of a homopolymer of analpha-olefin or a statistical copolymer comprising an alpha-olefin andat least one comonomer selected from alpha-olefins and diolefins. Thealphaolefins and diolefins are selected from those mentioned above.

The catalytic systems according to the invention are especially wellsuited to the manufacture of homopolymers of propylene and of copolymerscontaining in total at least 50% by weight of propylene, and preferably75% by weight of propylene.

The polymerisation may be performed according to any known process: insolution or in suspension in a solvent or an inert hydrocarbon diluent,such as those defined in relation to the preparation of the cocatalyticcomposition and which is preferably selected from butane, pentane,hexane, heptane, cyclohexane, methylcyclohexane or mixtures thereof. Inthese processes, it is possible, without discrimination, to use thecocatalytic composition in the form of a solution in the same diluent orto introduce it in the pure form into the polymerisation medium. It isalso possible to carry out the polymerisation in the monomer or one ofthe monomers maintained in the liquid state or alternatively in thegaseous phase. In this case, it is preferable to use the cocatalyticcomposition in pure form (without a diluent).

The polymerisation temperature is generally selected at between 20° and200° C., and preferably between 50° and 90° C., the best results beingobtained at between 65° and 85° C. The pressure is generally selected atbetween atmospheric pressure and 80 atmospheres, and preferably between10 and 50 atmospheres. This pressure is naturally dependent on thetemperature used.

The polymerisation may be performed in continuous or discontinuousfashion.

The preparation of so-called block copolymers may also be carried outaccording to known processes. It is preferable to use a two-stepprocess, consisting in polymerising an alpha-olefin, generallypropylene, according to the method described above forhomopolymerisation. The other alpha-olefin and/or diolefin, generallyethylene, is then polymerised in the presence of the still activehomopolymer chain. This second polymerisation may be carried out aftercompletely or partially removing the monomer which has not reactedduring the first step.

The quantity of solid constituent employed is determined in accordancewith its TiCl₃ content. It is generally selected in such a way that theconcentration of the polymerisation medium is greater than 0.01 mmol ofTiCl₃ per liter of diluent, of liquid monomer or of reactor volume, andpreferably greater than 0.05 mmol per liter.

The total quantity of cocatalytic composition employed is not critical;expressed with respect to the organoaluminium halide (A) which itcontains, this quantity is generally greater than 0.1 mmol per liter ofdiluent, of liquid monomer or of reactor volume, and preferably greaterthan 0.5 mmol per liter.

The ratio of quantities of solid constituent and cocatalytic compositionis not critical either. These quantities are generally selected in sucha way that the mole ratio of the quantity of organoaluminium halide (A)present in the composition to the quantity of titanium trichloridepresent in the solid constituent is between 1 and 30 mole/mole, andpreferably between 5 and 25 mole/mole. Under these conditions, and inview of the relatively small quantity of compound (ED) which thecocatalytic composition can contain (see above), the mole ratio of thiscompound (ED) to titanium trichloride in the catalytic system can bemaintained at very low values also, advantageously less than unity andpreferably between 0.1 and 0.5, thereby avoiding any undesirable sideeffect on the catalytic properties.

The molecular weight of the polymers manufactured according to theprocess of the invention may be adjusted by adding to the polymerisationmedium one or more molecular weight-adjusting agents such as hydrogen,diethylzinc, alcohols, ethers and alkyl halides.

The examples which follow serve to illustrate the invention.

The meaning of the symbols used in these examples, the units expressingthe parameters mentioned and the methods of measurement of theseparameters are clarified below.

α=catalytic activity expressed conventionally as grams of polymerinsoluble in the polymerisation medium, obtained per hour and per gramof TiCl₃ contained in the preactivated catalytic solid. This activity isassessed indirectly from determination of the residual titanium contentof the polymer by X-ray fluorescence.

fit=mole fraction of isotactic triads (sequenced linkage of threemonomeric propylene units in meso configuration) of the total polymer.This fraction is determined by ¹³ C NMR as described in Macromolecules,volume 6, No. 6, page 925 (1973) and in references (3) to (9) of thispublication.

I.I=isotacticity index of the polymer, assessed by the fraction of thelatter, expressed in % relative to the total quantity of the solidpolymer collected, which is insoluble in boiling heptane.

G=modulus of rigidity in torsion of the polymer, measured at 100° C. andfor a torsional angle of 60° of arc, the temperature of the mould beingfixed at 70° C. and the time of conditioning at 5 minutes (Standards BS2782 - part I - method 150A; ISO 458/1, method B; DIN 53447 and ASTM D1043). This modulus is expressed in daN/cm².

MFI=melt flow index measured under a load of 2.16 kg at 230° C. andexpressed in g/10 min (ASTM Standard D 1238).

ASG=apparent specific gravity of the insoluble polymer fraction,measured by packing down and expressed in g/l.

EXAMPLES 1 AND 2 AND EXAMPLES 3R TO 5R

(Examples 3R to 5R are given by way of comparison)

A. Preparation of the solid constituent based on complexed titaniumtrichloride

1. Reduction

90 ml of dry hexane and 60 ml of pure TiCl₄ are introduced under anitrogen atmosphere into an 800-ml reactor equipped with a 2-bladedstirrer rotating at 400 rpm. This hexane/TiCl₄ solution is cooled to 0(±1)° C. In the course of 4 h, a solution consisting of 190 ml of hexaneand 70 ml of diethylaluminium chloride (DEAC) is added while thetemperature of 0 (±1)° C. is maintained in the reactor.

After addition of the DEAC/hexane solution, the reaction mediumconsisting of a suspension of fine particles is kept stirring at 0 (±1)°C. for 15 min, is then brought to 25° C. in the course of 1 h andmaintained at this temperature for 1 h and thereafter brought to 65° C.in the course of approximately 1 h. The medium is kept stirring for 2 hat 65° C..

2. Prepolymerisation

The suspension obtained is then cooled to approximately 55° C. Propyleneat a pressure of 2 bars is then introduced into the gaseous atmosphereof the reactor. This introduction is continued for sufficient time(approximately 45 minutes) to obtain 70 g of polymerised propylene perkg of solid. The suspension of solid thus "prepolymerised" is thencooled to 40° C.

The liquid phase is then separated from the solid and the solid productis washed 7 times by means of 200 ml of dry hexane, with resuspension ofthe solid at each wash.

3. Treatment with the complexing agent

The "prepolymerised" reduced solid obtained is suspended in 456 ml ofdiluent (hexane), and 86 ml of diisoamyl ether (DIAE) are added. Thesuspension is stirred for 1 h at 50° C. The solid thus treated is thenseparated from the liquid phase.

4. Treatment with TiCl₄

The treated solid is resuspended in 210 ml of hexane, and 52 ml of TiCl₄are added; the suspension is kept stirring (150 rpm) at 70° C. for 2 h.The liquid phase is then removed by filtration and the solid (precursor)based on complexed titanium trichloride is washed 14 times with 270 mlof hexane.

5. Preactivation

74 g of the solid precursor (containing approximately 780 g of TiCl₃/kg) suspended in 280 ml of hexane, are introduced into an 800-mlreactor equipped with a paddle stirrer rotating at 150 rpm. 120 ml of asolution in hexane of a preactivator, prepared beforehand by mixing, perliter of hexane, 80 g of DEAC (compound (D)) and 176.2 g of n-octadecyl3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate marketed by CIBA-GEIGYunder the name Irganox 1076 (compound (I)), are introduced slowly (30minutes) into this reactor. The mole ratio between the compounds (D) and(I) employed for preparing the preactivator is hence 2, and the moleratio of the preactivator to the precursor (expressed in moles ofcompound (D) initially employed per mole of TiCl₃ present in theprecursor) is equal to 0.2.

The solution of preactivator is not introduced into the reactor until 15minutes after the gaseous evolution observed during mixing of thecompound (D) and the compound (I) has ceased.

The suspension thus treated with the preactivator is kept stirring for 1hour at 30° C.

After settling has taken place, the resulting catalytic solid isseparated and washed 5 times by means of 100 ml of dry hexane, withresuspension of the solid at each wash, and then dried by the passage ofa stream of nitrogen in a fluidised bed at 50° C..

The catalytic solid thereby obtained contains 616 g of TiCl₃ per kg.

B. Polymerisation of propylene in suspension in liquid monomer

1. Preparation of the cocatalytic compositions

To carry out Examples 1 and 2, pure liquid ethylaluminium dichloride(EADC) is added to pure liquid diethylaluminium chloride (DEAC) toobtain an ethylaluminium chloride (organoaluminium halide (A))possessing an atomic ratio (Cl)/(Al) equalling 1.05 (Example 1) and 1.02(Example 2).

Ethyl benzoate (EB) is added to this ethylaluminium chloride thuspreformed, in such a way that the mole ratio of the ethylaluminiumchloride to EB is equal to 60 (Example 1) and 57 (Example 2).

The cocatalytic compositions thereby obtained are maintained at 25° C.for 1 hour before being used in polymerisation.

To carry out Examples 3R to 5R (comparative), the procedure is as aboveexcept that, during the preparation of the cocatalytic compositions:

EB is added to the ethylaluminium chloride of Example 2 in such a waythat the mole ratio of the ethylaluminium chloride to EB is equal toonly 20 (Example 3R);

EB is added to pure liquid DEAC (atomic ratio Cl/Al=1.00) in such a waythat the mole ratio of the ethylaluminium chloride is equal to 57(Example 4R);

triethylaluminium is added to pure liquid DEAC to obtain anethylaluminium chloride possessing an atomic ratio Cl/Al equalling 0.95(mole ratio of the ethylaluminium chloride to EB =57) (Example 5R).

2. Polymerisation - Reference conditions

The following are introduced under a stream of nitrogen into a 5-1autoclave dried beforehand and maintained under a dry nitrogenatmosphere:

100 mg of catalytic solid;

a volume of cocatalytic composition such that the atomic ratio of thealuminium which it contains to the titanium contained in the catalyticsolid equals approximately 15;

hydrogen under partial pressure of 1 bar;

3 l of liquid propylene.

The reactor is maintained at 70° C. with stirring for 3 hours. Theexcess propylene is then outgassed and the polypropylene (PP) formed isthen recovered.

The results of the polymerisation experiments are collated in Table Ibelow.

                  TABLE I                                                         ______________________________________                                        Examples                                                                              1        2        3R     4R     5R(1)                                 ______________________________________                                        α 5447     5448     4500   5447   5050                                  fit     0.96     0.95     0.95   0.93   0.94                                  I.I     97.9     97.1     97.2   97     96.4                                  G       790      660      690    660    660                                   MFI     8.8      3.1      5.1    4.9    3.8                                   ASG     510      506      500    489    504                                   ______________________________________                                         (1) The cocatalytic composition of this example is unstable, and the          stated results are no longer obtained after only two days of ageing.     

Examination of this table shows that the best compromise of results isobtained with the systems containing the cocatalytic compositionsaccording to the invention (Examples 1 and 2).

EXAMPLE 6

A cocatalytic composition is prepared by adding to DEAC successivelyEADC and EB in such a way as to obtain an ethylaluminium chloride ofatomic ratio (Cl)/(Al) equal to 1.02, containing 0.017 mole of EB permole of ethylaluminium chloride. The efficacy of this composition, usedin polymerisation under the reference conditions 1 hour after beingprepared, is recorded in Table II below.

EXAMPLES 7 TO 12

The cocatalytic composition of Example 6 is divided into three fractions[(a), (b), (c)], which are stored at 0° C., 30° C. and 60° C.respectively, for variable periods before being used in polymerisationunder the reference conditions.

Table II records the conditions of storage of these compositions as wellas the results of the polymerisation tests.

                                      TABLE II                                    __________________________________________________________________________    Examples     6    7    8    9    10   11   12                                 __________________________________________________________________________    Cocatalytic composition                                                                         (a)  (a)  (b)  (b)  (c)  (c)                                Storage temperature (°C.)                                                           --   0    0    30   30   60   60                                 Storage period (days)                                                                      0    19   60   48   230  37   101                                Polymerisation results                                                        α      6089 5448 5751 6089 5750 5447 6469                               fit          0.96 0.96 0.95 0.94 0.94 0.96 0.94                               I.I          97.7 96.9 96.5 97.4 96.1 98.5 95.8                               G            714  676  688  686  670  648  685                                MFI          9    4.5  7    4.5  5.1  1.3  0.9                                ASG          520  511  506  514  511  508  506                                __________________________________________________________________________

EXAMPLE 13R

A cocatalytic composition is prepared by adding triethylaluminium and EBsuccessively to DEAC in such a way as to obtain a composition of atomicratio (Cl)/(Al) equal to 0.97, containing 0.017 mole of EB per mole ofethylaluminium chloride. When tested in polymerisation two days afterbeing prepared (reference conditions), this composition leads to theproduction, with an activity of 5447, of a sticky polymer whoseisotacticity index (I.I) is only 90.4% and in which the mole fraction ofisotactic triads (fit), measured by NMR, is only 0.89.

EXAMPLES 14R AND 15R

A cocatalytic composition is prepared by adding EADC and ethylene glycoldimethyl ether (Example 14R) or piperazine (Example 15R) successively toDEAC in such a way as to obtain an ethylaluminium chloride of atomicratio (Cl)/(Al) equal to 1.02, containing 0.02 mole of electron-donatingcompound per mole of ethylaluminium chloride.

Since the electron-donating compounds used in these examples are solubleneither in the organoaluminium halides nor in the inert hydrocarbondiluents, it is not possible to obtain homogeneous cocatalyticcompositions which are readily usable in polymerisation.

We claim:
 1. A cocatalytic composition capable of being stored,resulting from bringing an organoaluminium halide (A) into contact withan electron-donating organic compound (ED) selected from carboxylic acidesters, amides and ketones, the organoaluminium halide (A) having anatomic ratio halogen (X)/aluminium (Al) of greater than 1 and less than1.3, and the halide (A) and the compound (ED) having a mole ratio halide(A)/compound (ED) of greater than about
 20. 2. The cocatalyticcomposition according to claim 1, consisting essentially of the productresulting from bringing the electron-donating organic compound (ED) andthe organoaluminium halide (A) into contact.
 3. The compositionaccording to claim 1, wherein the electron-donating organic compound(ED) is brought into contact with the organoaluminium halide (A) in theabsence of alpha-olefin.
 4. The composition according to claim 1,wherein the electron-donating organic compound (ED) is brought intocontact with the organoaluminium halide (A) in the absence of solidcontaining a titanium halide.
 5. The composition according to claim 3,wherein the electron-donating organic compound (ED) is brought intocontact with the organoaluminium halide (A) under non-polymerisingconditions, in the absence of alpha-olefins and of solid containing atitanium halide.
 6. The composition according to claim 1, whereinorganoaluminium halide (A) is selected from the compounds correspondingto the overall formula ##STR2## in which R¹ and R² represent identicalor different radicals selected from alkyl, alkenyl, cycloalkyl, aryl,arylalkyl, alkylaryl, alkoxy and aryloxy radicals and at least one of R¹and R² represents a hydrocarbon radical;X is a halogen; m and n eachrepresent any number such that 0≦m<2 and 0≦n<2, and p represents anumber such that 1<p<1.3, the sum of m, n and p equalling
 3. 7. Thecomposition according to claim 6, wherein in the formula (I), R¹ and R²are selected from alkyl, alkoxy and aryloxy radicals, X is chlorine, mrepresents a number such 1≦m≦1.95 and p represents a number such that1<p≦1.15.
 8. The composition according to claim 1, wherein theorganoaluminium halide (A) is an alkylaluminium chloride possessing anatomic ratio chlorine/aluminium such that 1.01≦(Cl)/(Al)≦1.08.
 9. Thecomposition according to claim 8, wherein the alkylaluminium chloride isan ethylaluminium chloride.
 10. The composition according to claim 1,wherein the organoaluminium halide comprises the products of thereaction of halogenated alkylaluminium compounds with hydroxyaromaticcompounds in which the hydroxyl group is sterically hindered.
 11. Thecomposition according to claim 1, wherein the mole ratio halide(A)/compound (ED) is between 35 and
 150. 12. The composition accordingto claim 11, wherein the mole ratio halide (A)/compound (ED) is greaterthan 50 without exceeding
 90. 13. The composition according to claim 1,wherein the electron-donating organic compound (ED) is a liquid aromaticcarboxylic acid ester.
 14. The composition according to claim 1, whereinthe organoaluminium halide (A) is an alkylaluminium chloride possessingan atomic ratio (Cl)/(Al) of between 1.01 and 1.06 and in that thecompound (ED) is ethyl benzoate employed in a mole ratio halide(A)/compound (ED) of between 52 and
 75. 15. The composition according toclaim 1, wherein the compound (ED) is brought into contact with thehalide (A) preformed by prior mixing of organoaluminium compounds havinghalogen contents and in proportions suitable for conferring on thehalide (A) an atomic ratio (X)/(Al) of greater than 1 and less than 1.3.16. The composition according to claim 1, wherein the compound (ED) isintroduced into the halide (A) maintained in the liquid state.
 17. Thecomposition according to claim 1, wherein it takes liquid form.
 18. Acatalytic composition for the polymerisation of alpha-olefins,comprising:(a) a solid containing a titanium halide, (b) a cocatalyticcomposition according to claim
 1. 19. The composition according to claim18, wherein the solid (a) is a solid based on titanium trichloridecomplexed with an electron-donating compound.
 20. The compositionaccording to claim 19, wherein the solid (a) corresponds to the formula:

    TiCl.sub.3.(AlRCl.sub.2).sub.x.C.sub.y

in which R is an alkyl radical comprising from 2 to 6 carbon atoms; x isany number greater than 0.20; y is any number greater than 0.009; and Cis the complexing agent.
 21. The catalytic composition according toclaim 19, wherein the solid (a) has been subjected to an activationtreatment by means of a product of the reaction of an organoaluminiumcompound with a hydroxyaromatic compound in which the hydroxyl group issterically hindered.